It wasn't much of a system. The "shoebox" method of storing seed packets can become untidy. You need to sort through all the packets to find what you want. By sewing pockets in clear plastic A4 or US Letter sleeves and putting them in a ring binder it is easy to find the seeds you need.
Step 2: Divide the plastic sleeve into quarters
Use a bright color to make the lines easy to see.
Step 3: Cut bottom openings
Place a cardboard shield inside the plastic sleeve (I used part of a cereal box), then cut horizontally from the edges to about 12mm (a half inch) to the middle. Make your cut a little bit down from the dividing line.
Step 4: Sew along the lines
Step 5: Insert one seed packet per quarter
With small seeds such as lettuce or carrots, I sometimes put two packets in each section.
Step 6: Name the seeds
I used sticky notes but little plastic flags that are sticky on one end would work better, or even folded over tape.
Step 7: Put the pages in the ring binder
Step 8: The finished seed packet book
It is easy to see where the various seeds are.
Step 9: An enhancement
One small problem was that bigger seeds (bean, pumpkin, corn etc) tended to either make their pages sag or fall out the top. I use clothes pins to hold the pages shut unless I'm actually using the book. By having several clothes pins (any clip would work) they can be arranged to keep different pages closed.